CA1255648A - Conversion of a lower alkane - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention relates generally to the conversion of a lower molecular weight alkane to more valuable, heavier hydrocarbons,and more particularly concerns an aforesaid conversion which comprises the oxidative coupling of the alkane and the oxidative coupling catalyst employed therein.
The specification discloses an improved oxidative coupling catalyst comprising a reducible compound of lead, antimony, vanadium, tin, bismuth, cadmium, indium, manganese or thallium or a mixture thereof and a support comprising silica having a surface area less than about 175 m2/gm, wherein the reducible compound is at a level of from about 2 to about 50 weight percent, calcul? the oxide of the reducible metal and based on? of the catalyst. The present inven-tion is also an improved method for converting at least one feedstock alkane containing from 1 to 3 carbon atoms to more valuable, higher molecular weight hydrocarbons, comprising contacting the feedstock alkane with an oxygen-containing gas in a reactor in the presence of the afore-said oxidative coupling catalyst at a temperature in the range of from about 600°C to about 1000°C.

Description

fi~8 CONVERSION OF A LOWER ALKANE

BACKGROUND OE THE INVENTION

Field of the Invention This invention relates generally to the conversion of a lower molecular weight alkane to more valuable, heavier hydrocarbons, and more particularly concerns an aforesaid conversion which comprises the oxidative cou-pling of the alkane and the oxidative coupling catalystemployed therein.

Description of the Prior Art A major source of lower molecular weight alkanes is natural gas. Lower molecular weight alkanes are also present in coal deposits and are formed during numerous mining operations, in various petroleum processes and in the above- or below-ground gasification or liquefaction of coal, tar sands, oil shale and biomass.
It is highly desirable to convert lower molecular weight alkanes to more valuable and higher molecular weight materials and a number of attempts to do so have been reported. For example, G. E. Keller and M. M.
Bhasin (J. Catal. 73, 1982, 9-19) have shown that in the presence of catalysts methane can be converted to C2 hydrocarbons, but that the yields of ethylene and ethane are low and amount to only from 10 to 50 percent of the reacted methane. To improve the selectivity for the production of the desired C2 hydrocarbons and to suppress the undesirable further reaction of the C2 hydrocarbons initially formed to produce carbon dioxides, Keller and ~hasin propose a special reaction method: the catalyst is first charged with oxygen by the passage over it of a gas containing oxygen; then in a second step, the oxygen in the gas chamber of the catalytic reactor is replaced by an inert gas; in a third step, methane is fed over the catalyst which partially produces the desired reaction;

in a fourth and last step, an inert gas is again led through the reactor to supplant the residual methane and the resulting product, before the sequence of steps is repeated. In this process, depending on the catalyst used and the temperature selected, the selectivities for the production of C2 hydrocarbons range from about 5 to about 45%, and the selectivities for the production of C2 range from about 55 to 95%, with the conversions of methane ranging between 1 and 10%.
- 10 Keller and Bhasin arrive at the conrlusion that the ~ oxidative coupling is only highly selective to the higher - hydrocarbons when the reaction takes place in the absence of gas-phase oxygen and the oxidative coupling of the hydrocarbons should be caused by reaction with the lat-tice oxygen of the metal oxides, which are thus reduced by two valency stages. Since the lattice oxygen avail-- able in the catalyst is predetermined, for every measured unit of the catalyst only a limited quantity of hydrocar-bons can be reacted.
It is evident that the modus operandi in Keller and Bhasin is costly in terms of apparatus as well as being ~r simultaneously linked with small yields in space-time terms and high operating and investment costs. Moreover, the attainable methane conversions and/or the resultant space-time yields are too small for a commercial instal-lation according to the data of the authors. Further-more, the only products reported are C2 hydr6ocarbons.
Jones et al., U.S. Patents Nos. 4,443 ~ -9 disclose methods for synthesizing hydrocarbons containing as many as 7 carbon atoms from a ~ethane source which comprise contacting methane with a reducible oxide of antimony, germanium, bismuth, lead, indium or manganese. These patents also disclose that the reducible oxides can be supported by a conventional support material such as silica, alumina, titania, and zirconia. Specific sup-ports disclosed are Houdry HSC 534 silica, Cab-O-Sil,*
Norton alpha-alumina and Davison gamma-alumina. The * trade mark ranges of reaction temperatures disclosed in the aforesaid patents are from a lower limit of 500C to an upper limit of 800C.-1000C. In the disclosed pro-cesses, the reducible oxide is first reduced and is then regenerated by oxidi~ing the reduced composition with molecular oxygen, either in a second zone or by alter-nating the flow of a first gas comprising methane and the flow of an oxygen-containing gas. The highest yield of hydrocarbon products reported was only about 2.1% of the methane feed, when a reduclble oxide of manganese was ,~,, employedO
Furthermore, Baerns, West German Patent Application No. 3,237,079.2* discloses a method for the production of - ethane or ethylene by the reaction of methane and an oxy-~` 15 gen-containing gas at a temperature between 500C and 900C, at an oxygen partial pressure of less than about . . .
0.5 atmosphere at the reactor entrance, with a ratio of methane partial pressure-to-oxygen partial pressure greater than 1 at the reactor entrance and in the pres-~ 20 ence of a solid catalyst free of acidic properties. As `~ disclosed, the method can be performed with or without '~f' recycle of remaining unreacted methane. The highest molecular weight product formed in the disclosed method is propane, and the highest collective selectivity for the formation of ethane, ethylene and propane is onlyabout 65% of the methane converted.
Baerns discloses that oxides of the metals of Groups - III-VII of the Periodic Table are suitable for use as catalysts in the method disclosed therein and that the oxides of lead, manganese, antimony, tin, bismuth, thal-lium, cadmium and indium are particularly preferred.
Baerns further discloses that the metal oxides can be employed with or without a carrier and that specifically preferred carriers are alumina, silica, silicon carbide and titania. Specific examples of carrier materials dis-closed were formed from gamma-alumina having BET surface areas of 160-166 m /gm, silica having a BET surface area - * published 12 April 1984, P~B

of 290 m2/gm, bismuth oxide, aluminum silicate, and titania.

OBJECTS OF T~E INVENTION
It is therefore a general object of the present invention to provide a method for converting a lower molecular weight alkane to more valuable, heavier hydro-carbons which meets the aforementioned requirements and solves the aforementioned problems of prior art methods.
More particularly, it is an object of the present invention to provide a method for converting a lower molecular weight alkane to more valuable, heavier hydro-carbons with a high degree of conversion of the alkane.
It is another object of the present invention to provide a method for converting a lower molecular weight alkane to more valuable, heavier hydrocarbons with a high degree of selectivity for the production of heavier hydrocarbons.
It is a similar object of the present invention to provide a method for converting a lower molecular weight alkane to more valuable, heavier hydrocarbons which affords a high yield of heavier hydrocarbons.
Other objects and advantages of the present inven-tion will become apparent upon reading the following detailed description and appended claims, and upon refer-ence to the accompanying drawing.

SUM~lARY OF THE INVENTION
These objects are achieved by an improved oxidative coupling catalyst comprising a reducible compound of lead, antimony, vanadium, tin, bismuth, cadmium, indium, manganese or thallium or a mixture thereof and a support comprising silica having a surface area less than about 175 m2/gm, wherein the reducible compound is at a level of from about 2 to about 50 weight percent, calculated as the oxide of the reducible metal and based on the weight of the catalyst. The present invention is also an _5_ improved method for converting at least one feedstock alkane containing from 1 to 3 carbon atoms to more valu-able, higher molecular weight hydrocarbons, comprising contacting the feedstock alkane with an oxygen-containing gas in a reactor in the presence of the aforesaid oxida-tive coupling catalyst at a temperature in the range of from about 600C to about 1000C.

BRIEF DESCRIPTION OF THE DRAWING
For a more complete understanding of this invention, reference should now be made to the embodiments illus-trated in greater detail in the attached drawing and described below by way of examples of the invention. In the drawing r FIG. 1 iS a schematic illustration of a pre-ferred embodiment of the method of the present invention in which: (a) a methane feedstock is combined with air in the presence of an oxidation coupling catalyst of this invention and is initially partially converted to a mix-ture comprising ethane and ethylene; (b) the resulting product stream is subjected to an oligomerization treat-ment in which the ethylene in the product stream is cata-lytically aromatized to form heavy and light aromatics;
(c) the resulting heavy aromatics formed in the product stream in step (b) are separated from the product mix-ture; (d) the resulting light aromatics formed in theproduct stream in step (b) are separated from the product mixture; (e) after separation of a slip stream from the remaining product mixture, the remaining product mixture is recycled to step (a) for additional conversion of remaining unreacted feedstock alkane; and (f) at least a portion of the nitrogen and carbon dioxide components of the slip stream are separated from the slip stream and the remainder of the slip stream is then recycled to step ~a) for additional conversion of remaining unreacted feedstock alkane.
It should be understood that the drawing is a sche-matic illustration, and that in certain instances, ~%~

details which are not necessary for an understanding of the present invention or which render other details dif-ficult to perceive may have been omitted. It should be understood, of course, that the invention is not neces-sarily limited to the particular embodiments illustratedherein.

DETAILED DESCRIPTION OF THE DRAWING
INCLUDING PREFERR~D EMBODIMENTS
Turning first to E'IG. 1, there is shown schemati-cally a preferred embodiment of the method of this inven-tion. Methane, illustrative of a feedstock comprising at least one alkane containing from 1 to 3 carbon atoms is mixed with air, as a source of oxygen, and the resulting mixture is introduced through line 11 into a first reactor 12 where it is contacted with a catalyst of the present invention for the oxidative coupling of the aforesaid alkane. The effluent from the first reactor 12 is a gaseous product stream comprising carbon dioxide, nitrogen, any remaining unreacted feedstock alkane and oxygen, and ethane and ethylene, illustrative of alkane and alkene products having higher molecular weights than the feedstock alkane from which they are formed, and is introduced through line 13 into a second reactor 14, where it is contacted with a suitable oligomerization catalyst under aromatization conditions. The effluent from the second reactor 14 comprises carbon dioxide, nitrogen, any remaining unreacted feedstock alkane and oxygen, and higher molecular weight alkane and aromatic products, and is passed through line 15 and a first sepa-rator 17 where the separation of any higher boiling prod-ucts produced in the second reactor 14 is effected. The remaining lower boiling materials are then withdrawn as a gaseous mixture in line 18 from the first separator 17 and introduced into a second separator 19 where lower boiling normally liquid products and optionally at least a portion of the gaseous hydrocarbon products having molecular weights above the feedstock alkane from which they were ultimatley formed are separated. The gaseous effluent from the second separator 19, comprising carbon dioxide, nitrogen and any remaining unreacted feedstock alkane and oxygen, is then split into two streams. The first resulting stream is a major portion of the gaseous effluent from the second separator 19, and is recycled in line 23 as feedstock back to the first reactor 12. The second resulting stream is a minor portion of the gaseous effluent from the second separator 19, has the same com-position as the aforesaid first resulting stream, but is passed in line 24 through a third separator 25 where at least a portion of the remaining unreacted feedstock alkane, and ethane is removed therefrom and recycled through line 26 and line 23 as feedstock back to the first reactor 12.
It should be understood that FIG. 1 illustrates merely one preferred embodiment of the method and cata-lyst of this invention and that the present invention is not limited to the particular embodiment illustrated in FIG. 1.
Generally, a suitable feedstock for the method of this invention comprises at least one of methane, ethane and propane, preferably comprises methane and more pref-erably comprises a mixture of methane and ethane. Thus,a suitable feedstock for the method of this invention comprises natural gas, gases formed during mining opera-tions, in petroleum processes or in the above- or below-ground gasification or liquefaction of coal, tar sands, oil shale and biomass.
The oxygen-containing gas for use in the method of this invention can vary in molecular oxygen content from that of air to oxygen gas itself. Air or enriched air is a preferred source of molecular oxygen. The oxygen-con-taining gas should provide a gas-vapor effluent mixture from the oxidative coupling reactor containing (measured on a solid-free basis) from about 2 to about 8 volume ~z~

percent of oxygen, in order to avoid the flammability limits in such mixture.
The oxidative coupling reaction is performed at a temperature in the range of from about 600C. to about 1000C., preferably in the range of from about 700C to about 850Co The oxidative coupling step of the method of this invention is performed under a total absolute pressure preferably in the range of from about 1 atmo-sphere to about 10 atmospheLes, and more preferably in the range of from about 1 atmosphere to about 5 atmo-spheres. The ratio of the combined partial pressures of the feedstock alkanes containing from 1 to 3 carbon atoms in the feedstock-to-the oxygen partial pressure at the entrance of the reactor in the oxidative coupling step is preferably in the range of from about 2 1 to about 40:1 and more preferably in the range of from about 5:1 tc about 30:1. The combined partial pressures of the alkanes in the feedstock containing from 1 to 3 carbon atoms at the entrance to the oxidative coupling reactor is preferably in the range of from about 0.1 to about 10 atmospheres, and more preferably in the range from about 0~2 to about 5 atmospheres. The oxygen partial pressure at the entrance to the oxidative coupling reactor is preferably in the range from about 0.01 to about 5 atmo-spheres and more preferably in the range of from about0~02 to about 0.7 atmospheres. The oxygen partial pres-sure in the gaseous effluent from the reactor in the oxi-dative coupling step is preferably substantially zero.
The oxidative coupling step is performed preferably at a space velocity, calculated for a reaction pressure of one atmosphere absolute, of from about 100 to about 10,000 cubic centimeters of total feed gas comprising feedstock alkane containing from 1 to 3 carbon atoms per hour per cubic centimeter of catalyst and more preferably at a space velocity of from about 500 to about 5000 cubic centimeters of total feed gas comprising feedstock alkane containing from 1 to 3 carbon atoms per hour per cubic r _9_ centimeter of catalyst. For the purposes of this definition of the space velocity, the feedstock al~ane comprises from about 10 volume percent to about 80 volume percent of the total feed gas.
The catalyst of this invention employed in the oxi-dative coupling step of the method of this invention com-prises a reducible compound of lead, antimony, germanium, vanadium, tin, bismuth, cadmium, indium, manganese, thal-lium, or a mixture thereof. Preferably, the reducible compound employed is an oxide, sulfide, sulfate, or car-bonate of lead, antimony, germanium, vanadium, tin, bis-muth, cadmium, indium, manganese, thallium, or a mixture thereof. The oxidative coupling catalyst more preferably comprises a reducible compound of lead and most prefer-ably comprises a lead oxide. If a reducible compound oflead is present, the presence of additional reducible compounds of other metals, such as zirconium and titanium, which themselves are not effective catalysts, serves to promote the activity of the lead compound in the oxidative coupling reaction.
The oxidative coupling catalyst of this invention additionally comprises a silica support. Preferably, the support of the oxidative coupling catalyst of this inven-tion is silica. Such support has a surface area in the range of from about 1 m2/gm to about 175 m2/gm, and pref-erably in the range of from about 5 m2/gm to about 75 m /gm-The reducible compound component of the oxidative coupling catalyst of this invention comprises preferably from about 2 weight percent to about 50 weight percent of the oxidative coupling catalyst, and more preferably from about 10 weight percent to about 30 weight percent oE the oxidative coupling catalyst, calculated as the reducible metal oxide and based on the total weight of the oxida~
tive coupling catalyst.
The oxidative coupling catalyst of this invention can be prepared by impregnation of the aforesaid support with at least one precursor of the reducible metal compound. Any convenient, conventional impregnation technique can be employed for this purpose. For example, a soluble compound of the metal of the reducible metal oxide can be added to a sol or gel of the silica. This composition is then thoroughly blended into the sol or gel mixture, and subsequently co-gelled by the addition of a dilute ammonia solution. The resulting co-gelled material is then dried. In another method of prepara-tion, the silica is gelled, dried, and cooled and theresulting material is then impregnated with one or more solutions of a soluble compound of the metal of the reducible metal oxide.
Preferably, as will be described hereinbelow, the support containing the reducible metal compound or pre-cursor thereof is calcined, regardless of the method of preparation used. In such case, the calcination condi-tions are preferably calcining at a temperature of from about 500C to about 1050C for from about 2 hours to about 36 hours and more preferably calcining in air at a temperature of from about 950C to about 1050C for from about 4 hours to about 20 hours. More preferably, the support is also calcined prior to incorporating the redu-cible metal compound or its precursor therein. In such case, the catalyst is calcined preferably at a tempera-ture of from about 800C to about 1100C for from about 2 hours to about 36 hours and more preferably at a tempera-ture of from about 950C to about 1050C for from about 4 hours to about 16 hours.
It has been found that the selectivity of the oxida-tive coupling catalyst for the formation of coupled prod-ucts can be increased by the additional incorporation of an alkali metal component into the support. The presence of the alkali metal component in the oxidative coupling catalyst also permits the concentration of the reducible metal component in the catalyst to be reduced without decreasing the selectivity of the catalyst for the forma-~11--tion of coupled products. Preferably, the metal of thealkali metal component is sodium, potassium or lithium.
The alkali metal component is present in the catalyst at a concentration of preferably from about 0.1 to about 6 weight percent, more preferably from about 0.5 to about 3 weight percent, calculated as the alkali metal oxide and based on the weight of the catalyst. A compound of the alkali metal can be deposited by any convenient, conven-tional technique such as impregnation or spray drying, before, during or after deposition of the metal of the reducible metal component on the catalyst support. Upon calcination, the alkali metal component is converted to the form of its metal oxide.
The gaseous mixture resulting from the oxidative coupling reaction comprises any remaining unreacted feed-stock alkane and oxygen and saturated and unsaturated aliphatic hydrocarbon products having higher molecular weights than the feedstock alkane from which they were formed. In addition, if air is employed as the source of molecular oxygen in the oxidative coupling step of the method of the present invention, the effluent from the oxidative coupling step also contains nitrogen and carbon dioxide.
In order to increase the conversion of the feedstock alkane in the oxidative coupling step and the yield of the desired products therefrom, it is desirable to recycle the unconverted feedstock alkane to the oxidative coupling step in a preferred embodiment of the method of this invention. However, recycle of the entire gaseous product mixture from the oxidative coupling reaction to the oxidative coupling step results in a decrease of both the selectivity for the formation of coupled products and the yield of coupled products. Although the presence of saturated coupled products such as ethane in the feed to the oxidative coupling reaction and, hence, in the product mixture recycled to the oxidative coupling reac-tion affords a surprising increase in the selectivity for both the formation of coupled products and the yield of coupled products in the oxidative coupling step, the presence of unsaturated coupled products such as ethylene and acetylene in the feed to the oxidative coupling reac-tion and, hence, in the recycled product mixture, has asubstantial deleterious effect on the selectivity for the formation of and yield of coupled products in the oxida-tive coupling step. Thus, in order to increase the con-version of the feedstock alkane and yield of the desired coupled products therefrom, the recycled gaseous mixture must be relatively free of unsaturated coupled products.
Thus, in a preferred embodiment of the method of this invention, prior to being recycled, the gaseous product mixture from the oxidative coupling reaction is contacted with an oligomerization catalyst under aromati-zation conditions in order to remove unsaturated coupled products therefrom. Surprisingly, the use of certain acidic oligomerization catalysts permits substantially complete removal of the unsaturated hydrocarbons even at atmospheric pressure and from the dilute hydrocarbon streams from the oxidative coupling reaction. The aroma-tization conditions include a temperature preferably in the range of from about 50C to about 500C and more preferably in the range of from about 200C to about 400C. The aromatization conditions also include a total absolute pressure preferably in the range of from about l atmosphere to about lO atmospheres and more preferably in the range of from about 1 atmosphere to about 5 atmo-spheres. The aromatization conditions also include a space velocity, calculated for a reaction pressure of one atmosphere absolute, preferably in the range of from about lO0 to about 5,000 cubic centimeters of the gaseous mixture per hour per cubic centimeter of the oligomeriza-tion catalyst and more preferably in the range of from 35 about 200 to about 2,000 cubic centimeters of the gaseous mixture per hour per cubic centimeter of the oligomerization catalyst.

The oligomerization catalyst comprises a solid having acidic sites and comprising a molecular sieve, a pillared smectite or vermiculite clay or a combination thereof, or a combination thereof with an amorphous refractory inorganic oxide. Suitable molecular sieves for use in the oligomerization catalyst employed in the method of this invention include a crystalline alumino-silicate, crystalline borosilicate, or de-aluminated crystalline aluminosilicate, or combination thereof.
suitable crystalline aluminosilicate includes natural or synthetic chabazite, clinoptilolite, erionite, mordenite, zeolite A, zeolite L, zeolite X, zeolite Y, ultrastable zeolite Y, zeolite omega, or a ZSM-type zeolite such as ZSM-5, ZSM-ll, ZSM-12, ZSM-35, ZSM-38 or ZSM-48.
Mordenite-type crystalline aluminosilicates have been discussed in the patent art, for example, in Kimberlin, U.S. Patent No. 3,247,098; Benesi et al., U.S.
Patent No. 3,281,483; and Adams et al., U.S. Patent No.
3,299,153. Synthetic mordenite-type crystalline alumino-silicates, designated as Zeolon, are available from the Norton Company of Worcester, Massachusetts. Another example of a crystalline molecular sieve that is suitable for use in the oligomerization catalyst employed in the method of the present invention is a Y-type zeolitic crystalline aluminosilicate. Y-type, zeolitic molecular sieves are discussed in U.S. Patent No. 3,130,007.
Ultrastable, large-pore, Y-type, zeolitic crystal-line aluminosilicate material is also suitable for use in the oligomerization catalyst in the method of this inven-tion and is described in U.S. Patents Nos. 3,293,192 and 3,449,070. By large-pore material is meant a material that has pores which are sufficiently large to permit the passage thereinto of benzene molecules and larger mole-cules and the passage therefrom of reaction products.
The ultrastable, large-pore, Y-type, zeolitic crystalline aluminosilicate material that is suitable for use in the oligomerization catalyst employed in the method of this invention exhibits a cublc unit cell dimension and hydroxyl infrared bands that distinguish it from other aluminosilicate materials. The cubic unit cell dimension of the aforesaid ultrastable, large-pore, crystalline aluminosilicate is within the range of about 24.20 A to about 24.55 A. The hydroxyl infrared bands obtained with the aforesaid ultrastable, large-pore, crystalline aluminosilicate material are a band near 3,745 cm (3,745 + 5 cm ), a band near 3,695 cm 1 (3,690 ~ 10 cm 1), and a band near 3,625 cm 1 (3,610 + 15 cm 1~. The band near 3,745 cm 1 may be found on many of the hydro-gen-form and de-cationized aluminosilicate materials, but the band near 3,695 cm and the band near 3,625 cm are characteristic of the aforesaid ultrastable, large-pore, Y-type, zeolitic crystalline aluminosilicate material that is used in the catalyst of the present invention.
The ultrastable, large-pore, Y-type, zeolitic crystalline aluminosilicate material is also characterized by an alkaline metal content of less than 1%.
Other molecular sieve materials that are useEul in the catalyst employed in the method of the present inven-tion are ZSM-type crystalline aluminosilicate molecular sieves. Suitable crystalline aluminosilicates of this type typically have silica-to-alumina mole ratios of at least about 12:1 and pore diameters of at least 5 A. A
specific example of a useEul crystalline aluminosilicate zeolite of the ZSM-type is ZSM-5, which is described in detail in U.S. Patent No. 3,702,886. Other crystalline aluminosilicate zeolites of the ZSM-type contemplated according to the invention include ZSM-ll, which is described in detail in U.S. Patent No. 3,709,979; ZSM-12, which is described in detail in U.S. Patent No.
3,832,449; ZSM-35, which is described in U.S. Patent No.
4,016,245; and ZSM-38, which is described in detail in U.S. Patent No. 4,046,859. A preferred crystalline aluminosilicate zeolite of the ZSM-type is ZSM-5.

Dealuminated crystalline aluminosilicate zeolites having higher silica-to alumina mole ratios than in those formed by available synthesis of crystalline aluminosili-cate zeolites are also suitable for use in the oligomeri-zation catalyst of the method of the present inventionand can be produced by the removal of aluminum from the structural framework of the crystalline aluminosilicate zeolite by appropriate chemical agents. A considerable amount of work on the preparation of aluminum deficient faujasites has been performed and is reviewed in Advances in Chemistry, Series No. 121, "Molecular Sieves," G. T.
Kerr, American Chemical Society, 1973. Specific methods for preparing dealuminized zeolites are described in the following, and reference is made to them for details of the method: Catalysis by Zeolites (International Sympo-sium on Zeolites, Lyon, September 9-ll, 1980), Elsevier Scientific Publishing Co., Amsterdam, 1980 (dealuminiza-tion of zeolite Y with silicon tetrachloride); U.S.
Patent No. 3,442,795 and British Patent No. 1,058,188 (hydrolysis and removal of aluminum by chelation);
British Patent No. 1,061,847 (acid extraction of alu-minum); U.S. Patent No. 3,493,519 (aluminum removal by steaming and chelation); U.S. Patent No. 3,591,488 (alu-minum removal by steaming); U.S. Patent No. 4,273,753 (dealuminization by silicon halides and oxyhalides); U.S.
Patent No. 3,691,099 (aluminum extraction with acid);
U.S. Patent No. 4,093,560 (dealuminization by treatment with salts); U.S. Patent No. 3,937,791 (aluminum removal with Cr(III) solutions); U.S. Patent No. 3,506,400 (steaming followed by chelation); U.S. Patent No.
3,640,681 (extraction of aluminum with acetylacetonate followed by dehydroxylation); U.S. Patent No. 3,836,561 (removal of aluminum with acid); DE-OS 2,510,740 (treat-ment of zeolite with chlorine or chlorine-contrary gases 35 at high temperatures), Dutch Patent No. 7,604,264 (acid extraction), Japanese No. 53,101,003 (treatment with EDTA
or other materials to remove aluminum) and J. Catalysis, 54, 295 (1978) (hydrothermal treatment followed by acid extraction).
An additional molecular sieve that can be used in the oligomerization catalyst of the present invention is a crystalline borosilicate, which is described in Klotz, U.S. Patent No. 4,269,813 ~ ah~ e~ s~pee~
-i-~E~ ~te~-h~n b~ r~e-. A suitable crystalline borosilicate is a molecular sieve material having the following composition in terms of mole ratios of oxides:

o.g + 0.2 M2~n B2O3 ySiO2 2 wherein M is at least one cation having a valence of n, y is within the range of 4 to about 600, and z is within the range of 0 to about 160, and providing an X-ray pat-tern providing the following X-ray diffraction lines and assigned strengths:

d, AngstromsAssigned Strength 11.2 + 0.2 W - VS
: 10.0 + 0.2 W - MS
5-97 + 0.07 W - M
3.82 + 0.05 VS
3.70 + 0.05 MS
3.62 + 0.05 M - MS

2.97 + 0.02 W - M
1.99 + 0.02 VW - M

Suitable methods for preparing the aforesaid crystalline borosilicate molecular sieve are disclosed in Klotz, U.S.
Patent No. 4,269,813 and in Haddid, European Patent Application No. 82303246.1 which was published on January 5, 1983,corresponds to Canadian Patent 1,185,953 issued April 23, 1985.
Pillared smectite and vermiculite clays, which are also suitable for use in, or as, the oligomerization catalyst employed in the method of this invention, are often referred to in the literature as pillared interlayered clays and occasionally as molecular sieves.
The smectite clays comprise montmorillonite, beidellite, montronite, volchonskoite, hectorite, saponite, steven-site, sauconite and pimelite. Some pillared smectite and vermiculite clay materials that are suitable for use in the support of the catalyst employed in the method of this invention, and methods for preparing such clays, are disclosed in Vaughan et al., U.S. Patent No. 4,176,090;
Shabria et al., U.S. Patent No. 4,216,188; Shabtai, U.S.
Patent No. 4,238,364; D'Aniello, U.S. Patent No.
4,380,510; Pinnavaia, "Intercalated Clay Catalysts," Sci-ence, Vol. 220, pages 365-371 (April 22, 1983) and Vaughan et al., "Preparation of Molecular Sieves Based on Pillared Interlayered Clays (PILC)," Fifth International Conference on Zeolites, pages 94-101 and in the refer-ences cited therein. Preferably, a suitable pillared smectite or vermiculite clay comprises a multiplicity of cations interposed between the molecular layers of the clay and maintaining the spacing between the molecular layers in the range of from about 6 A to about 10 A at a temperature of at least 300C. in an air atmosphere for at least 2 hours.
Preferably, when the oligomerization catalyst com-prises an aforesaid molecular sieve material or an afore-said pillared smectite or vermiculite clay material or acombination thereof, the oligomerization catalyst also comprises a porous amorphous refractory inorganic oxide comprising an oxide of an element from Groups IIA, IIIA, IIIB, IVA or IVB of the Periodic Table. In such cases, the concentrations of the amorphous inorganic oxide and of the molecular sieve material and/or pillared smectite or vermiculite clay material are not critical. Prefer-ably, the amorphous refractory inorganic oxide content is at least high enough to give the oligomerization catalyst sufficient strength and integrity so that it can be employed in the method of the present invention without appreciable damage to the catalyst. In such case, the total concentration of the molecular sieve material and/or pillared smectite or vermiculite clay material in such mixture is preferably from about 5 to about 95 weight percent, and the total concentration of the amor-phous refractory inorganic oxide in the mixture is pref-erably from about 5 to about 95 weight percent, based on the weight of the support.
Preferably, when the oligomerization catalyst com-prises a mixture of a molecular sieve and/or pillared smectite or vermiculite clay and an amorphous refractory inorganic oxide, the oligomerization catalyst is in the form of a dispersion of the molecular sieve component and/or pillared smectite or vermiculite clay component in a matrix of the amorphous refractory inorganic oxide.
Such dispersions can be prepared by well-known tech-niques, such as blending the molecular sieve component and/or pillared smectite or vermiculite clay component, preferably in finely-divided form, into a sol, hydrosol or hydrogel of the amorphous reEractory inorganic oxide, and then adding a gelling medium, such as ammonium hydroxide, and stirring to produce a gel. Alternately, the molecular sieve component and/or pillared smectite or vermiculite clay component is blended into a slurry of the amorphous inorganic oxide. In either case, the resulting mixture can be dried, shaped, if desired, and then calcined to form the final support component. A
less preferred, but still suitable, method for preparing a suitable dispersion of the molecular sieve component and/or pillared smectite or vermiculite clay component in the amorphous refractory inorganic oxide is to dry-blend particles of each, preferably in finely-divided form, and then to conduct any desired shaping operations, such as pelletizing or extrusion; the resulting mixture is then calcined.
The oligomerization catalyst employed in the method of this invention comprises a solid having acidic sites.
Consequently, it is highly preferred that the aforesaid molecular sieve or pillared clay materials containing exchangeable cations and employed in the oligomerization catalyst are in their proton-exchanged forms. The proton forms of these materials are particularly effective at the low pressures employed in the oligomerization step of the method of this invention.
The aforesaid molecular sieve and pillared clay materials could also be in their metal-exchanged or metal-impregnated forms, provided that such metal-con-taining materials still have acidic properties. In suchcase, the metal employed should be one, such as zinc, which promotes the oligomerization-aromatization activity of the catalyst. Any convenient, conventional cation-ex-change or cation-impregnation technique can be employed for this purpose.
Suitable conditions for drying the above-described supports comprise a temperature in the range of from about 90C. to about 200C. and a drying time of from about 0.5 to about 30 hours. Suitable calcination condi-tions in such methods comprise a temperature in the rangeof about ~80C. to about 760C. and a calcination time of from about 2 to about 5 hours. Preferred drying and cal-cination conditions are a temperature of about 120C. for about 1-2 hours and a temperature of about 538C. for about 1-2 hours, respectively.
The gaseous mixture resulting from the oligomeriza-tion reaction comprises any remaining unreacted feedstock alkane and oxygen and a heavy aromatics product, a light aromatics product and at least one higher molecular weight saturated aliphatic hydrocarbon product. Prior to recycling the unreacted feedstock alkane component of this mixture to the oxidative coupling step, the desired hydrocarbon products are separated from it. This can be effected using any convenient, conventional method. One suitable method to accomplish this separation involves first separating the higher boiling, liquefiable products such as alkylbenzenes and alkylnaphthalenes by scrubbing the gaseous mixture in a suitable solvent at a sufficiently low temperature, such as a cooled oil scrubber, such that the aforesaid liquifiable products are selectively dissolved in it. The resulting liquefied products are recovered from the oil scrubber, for example, by distillation of the scrubbing oil. The remaining gaseous components of the product stream com-prise remaining unreacted feedstock alkane and oxygen and lower boiling products, such as lighter aromatics and saturated aliphatics, and pass through the oil scrubber as a gaseous mixture.
The lower boiling products are next separated from this mixture by any convenient, conventional technique.
One highly effective, novel technique involves passing the mixture through a charcoal bed. The unreacted feed-stock alkane and oxygen pass through the charcoal bed faster than do the products and are recycled to the oxi-dative coupling step before the products saturate and emerge from the bed. When the bed becomes saturated with the products/ the products begin to emerge from the bed, and the bed is removed from service and replaced in ser-vice by a fresh charcoal bed. The lower boiling products are then removed from the saturated bed and collected.
This separation step can be performed either by removing the bed from service when the lowest boiling product, for example, ethane, begins to emerge from the bed or, as illustrated in FIG.I, by removing the bed from service when higher boiling (but still low boiling~ products, for example, C3+ hydrocarbons, begin to emerge from the bed.
The adsorption or saturation step is conducted at a lower temperature than the desorption or product-removal step. The gases enter the charcoal bed at a temperature, for example, below about 65C and at substantially atmos-pheric pressure. Under these conditions as much as 20-30 percent of the weight of the bed is covered by adsorbed product. ~hen the bed can hold no more hydrocarbon as shown by the presence of higher hydrocarbons in the effluent gas from the charcoal bed, the feed gas is stopped and superheated steam is passed into the bed. As the bed heats up, it desorbs hydrocarbons which pass out of the bed with excess steam and are condensed out in a S separate operation. When the bed has been heated to some temperature preferably in the range of 105-300C. and desorption of hydrocarbons has diminished substantially, the charcoal bed is cooled down and then returned to ser-vice. Any oleophilic charcoal works well as do certain hydrophobic clays. In particular, coconut and bituminous charcoal have been shown to be both highly effective and inexpensive.
When the oxygen-containing gas comprises air, the gaseous mixture which remains after the step of recov-ering the lower boiling products comprises nitrogen andcarbon dioxide in addition to remaining unreacted feed-stock alkane and oxygen. Thus, nitrogen and carbon dioxide would build up in the recycled portion of the feed to the oxidative coupling step. This buildup of nitrogen and carbon dioxide in the recycle to the oxida-tive step can be eliminated conveniently by separating a slip stream from the recycle gas and venting a small por-tion, for example, 10 percent, of the recycle gas before the recycle gas is returned to the oxidative coupling step. However, in addition to nitrogen and carbon dioxide, the gas vented also contains some unreacted feedstock alkane. In order to maximize the conversion of the feedstock alkane to coupled products, it is desirable to separate the unreacted feedstock alkane component from the slip stream before it is vented and recycle the sepa-rated feedstock alkane to the oxidative coupling step.
This separation can be effected by any convenient, con-ventional technique. One highly effective, novel tech-nique involves passing the slip stream through a second charcoal bed. The nitrogen passes through the charcoal bed faster than does the unreacted feedstock alkane and is vented before the unreacted feedstock alkane saturates and emerges from the bed. When the bed becomes saturated with feedstock alkane, the feedstock alkane begins to emerge from the bed, and the bed is removed from service and replaced in service by a fresh charcoal bed. The feedstock alkane is then removed from the saturated bed and recycled to the oxidative coupling step.
For reclaiming feedstock alkane from the slip stream, a somewhat different mode of operating the char-coal bed is more advantageous than that described herein-above. In this case, because of the low adsorptivecapacity that charcoals have for methane, it is desirable to use rapid adsorption~desorption cycles, without exter-nally changing the temperature of the bed. It has been advantageous when such beds become saturated with methane, ethane and carbon dioxide (the nitrogen having been discharged) at a temperature up to 65C and substan-tially atmospheric pressure absolute, to remove adsorbed methane by evacuating the bed. With progressive evacua-tion down to about 28-29 inches of mercury vacuum, methane, carbon dioxide, and ethane are removed sepa-rately and sequentially, thus permitting an effective separation of such components. Methane and, if desired, higher hydrocarbons are returned to the recycle system;
while carbon dioxide is selectively rejected.
The present invention will be more clearly under-stood from the following specific examples.

Examples 1-149 demonstrate significant parameters of the oxidative coupling catalyst of this invention and of the oxidative coupling reaction of the method of this invention. In each of Examples 1-149, a stream of methane and air was passed through a heated quartz tube (except Examples 28-31 where a ceramic reactor was used) having an inside diameter of 1.43 centimeters and a length of from 10 to 43 centimeters and, in all cases except Examples 1-4 and 28-31, whose internal volume in the middle of the tube was filled with solid particles or pellets. The reaction pressure was approximately one atmosphere absolute. The product gas effluent from the tube was cooled with an ice bath condenser and analyzed.
The experimental parameters employed in Examples 1-149 and the results therefrom are presented in Tables 1-19.
In all cases except Examples 1-4 and 28-31, the units of space velocity are the volume (in cubic centimeters) of the combination of methane and air fed to the reactor per hour per cubic centimeter of catalyst in the tube. In Examples 1-4 and 28-31, the space velocity is the volume (in cubic centimeters) of the combination of methane and air fed to the reactor per hour per the inside volume (in cubic centimeters) of the reactorO Each of the product selectivity, selectivity for the formation of coupled products (C2+) and yield of C2+ (the product of methane conversion multiplied by the selectivity for the forma-tion of C2+ divided by 100) is reported as mole percent of the carbon in methane in the feed that is converted.
C4+ in the tables refers to gaseous products containing ~ at least ~ carbon atoms.
~ In Examples 1-4, the quartz tube was empty, and very _ little oxygen was consumed even at the highest reaction temperature, leading to little consumption of methane.
However, the selectivity for the formation of coupled products (C2+), based on the amount of methane consumed, was substantial even though most oxides of carbon appeared as carbon monoxide.
In Examples 5-10, when the tube was filled with pel-lets o~ Calsicat D (a product of Mallinckrodt, Inc. of Erie, Pa.), a preferred silica support for the preferred oxidative coupling catalyst, when a reaction temperature of at least 850C was employed, nearly all oxygen was consumed, and product selectivity for the formation of coupled product was moderate at 53~. The conversion to coupled products increased as the reaction temperature was increased, with ethylene predominating as the coupled * ~rade mark ~,, product. The selectivity for the formation of coupled products also increased at a given reaction temperature as the CH~/O2 mole ratio increased.
r~hen ceramic alumina chips were employed as the tube packing, as indicated in Table 3 for Examples 11-13, oxygen consumption was less, but selectivity for the for-mation of coupled products (C2+) was appreciably better (67-88%) than when Calsicat D was employed as the tube packing. However, high temperatures of the order of 890-945C were required to increase oxygen consumption, at which temperatures methane reforming, as evidenced by CO formation, increased substantially.

Example 1 2 3 4 Tube Packing Empty Tube Reactor Temp. (C) 700800 850 900 Space Velocity 480480 480 480 CH4/O2 (mole ratio)9.7/19.7/1 9.7/1 9.7/1 2 Conversion (mole %)0.2 4 12 29 CH4 Conversion (mole %) - 0.4 1.7 4.5 Product Selectivity C2 0 o o 3 C3 s C4 s+
Selectivity to C~

Yield of C~
nil0.3 1.1 2.5 Examp]e 5 6 7 8 9 10 Tube Packing Calsicat D Silica Reactor Temp. (C) 700800 850 900 900 800 Space Velocity120012001200 1200 lOO0 1000 CH4/O2 (mole ratio) 9.6/19.6/19.6/1 9.6/127/127/1 2 Conversion (mole %) 4.6 49 94 98+ 97+ 97+
CH4 Conversion (mole %) 0.14.7 10 12 5.5 4.1 Product Selectivity CO 7~ 44 25 22 19 35 20 C3 s -C4 s~
Selectivity to C

Yield of C +
nil1.7 5.3 6.7 3.6 1.9 Example 11 12 13 Tube Packing Ceramic Chips Reactor Temp. (C) 851 889 945 Space Velocity169616961696 CH4/O2 (mole ratio3 24/1 24/1 24/1 2 Conversion (mole %) 14.3 4.1 57 CH4 Conversion (mole %) 0.4 0.6 3.9 Product Selectivity C3's C4 s+
Selectivitv to C
~.
71 ~8 67 Yield of C
0.3 0.5 2.6 A tube packing of l percent by weight of potassium bromide on Calsicat D silica ~the silica was dispersed in an aqueous solution of potassium bromide; the solution was evaporated; and the silica was then dried and cal-cined) was employed in Examples 14-17 (Table 4) and was approximately as active and selective as Calsicat D
alone. Celite 408, a diatomaceous silica and a product of Johns Manville Company, was employed as the tube packing in Examples 18-21 (Table 5) and afforded rela-tively poor selectivity. Zirconia containing 2 percent by weight of alumina was employed as the tube packing in Examples 22-25 (Table 6) and promoted only formation of : carbon oxides. Alpha Alumina was employed as the tube ~ packing in ~xample 26 (Table 6) and afforded good activity but relatively low selectivity. Mordenite (Norton Zeolon lO0) was employed as the tube packing in Example 27 (Table 7) and formed little coupl2d product but afforded copious coking. A ceramic -alumina tube, not containing any tube packing, was employed in Examples 20 28-31 (Table 7) and was somewhat active at low space velocity and high reaction temperatures and afforded high selectivities for the formation of C2 and C3 products.
Magnesiu~ aluminum borate, a mixed oxide, was employed as the tube packing in Examples 32-35 (Table 8) and was only moderately active and afforded only moderate selectivity for the formatlon of coupled products.
In Examples 36-49, several forms of tube packings of lead oxide on various supports were employed. In Exam-ples 36-38 (Table 9), lead oxide on -alumina having a surface area of 31 m2/g was highly active in catalyzing the conversion of oxygen even at relatively low reaction temperatures, but with relatively poor selectivities of 44-55% for the production of coupled products. By con-trast, a low surface area silica (Examples 39-40) was highly selective.

* trade mark Example 14 15 16 17 Tube Packing1% KBr/Calsicat D Silica Reactor Temp. (C)700 800 850 900 Space Velocity120012001200 1200 CH4/02 ( mole ratio) 10/1 10/1 10/1 10/1 2 Conversion (mole %~ 81 98+ 98+ 98+
CH4 Conversion (mole %) 6.9 13 14 16 Product Selectivity C 's 0 2 3 4 20 C4's - - ~ -Selectivity to C~

Yield of ~
1.1 6.6 7.6 9.3 Example 18 19 20 21 Tube Packing Celite 408 Reactor Temp. (C) 700 800 850 900 Space Velocity 1200 1200 1200 1200 CEI4/02 ( mole ratio) 10/1 lO/l 10/l lO/l 2 Conversion (mole %) ~2 97+ 98+ 98+
CH4 Conversion (mole %) 3.2 6.8 7.2 8.0 Product Selectivity C 's 0 0 0 0 C ' s ~
Selectivity to C~

Yield of C~
0.4 0.5 0.7 1.1 ~ ~3~

Example 22 23 24 2526 Tube Packing ZrO~ + 2% Al~O~ ~-Alumina Reactor Temp. (C)700 800 850 850 800 Space Velocity480048004800 12008700 CH4/O2 (mole ratio) 2/1 2/1 2/1 10/1 19.5/1 O~ Conversion (mole %) 100 100 100 100100 CH4 Conversion (mole %) 26 28 33 11 Product Selectivity CO 20 28 35 6450.4 C2 81 72 65 3634.5 C2H4 0 0 0 07.2 C2 6 015.6 C3's 0 0 0 00.6 C4 s Selectivitv to C +

Yield of C +

Example Mor-Tube Packingdenite Empty Ceramic Reactor Reactor Temp. (C)833 840 885 937 915 Space Velocity 8700 1696 1696 1696 848 CH4/O2 (mole ratio) 20/1 24.1/1 24.1/1 24.1/1 29.1/1 2 Conversion (mole %) 92.5 3.8 7.419.743.2 CH4 Conversion (mole ~) 4.4 nil 0.51.8 4.1 Product Selectivity CO 51.9 - - 19.3 22.7 2 43.9 _ 0.6 C2 4 92.2 20.433.629.1 C2H6 4.2 - 64.833.935.6 C3's - 7.8 14.811.88.3 C4's+ - - - 1.4 3.7 Selectivity to C~
4.2 100 10080.776.7 Yield of C
0.18 nil 0.51.5 3.1 Example 32 33 34 35 Tube PackingMa~nesium Aluminum Borate Reactor Temp. C 811 851 846 845 Space Velocity1695 1695 848 424 CH4/02 (mole ratio)22.6/1 22.6/1 24.9/1 30.1/1 10 2 Conversion (mole %) 39.9 38.0 63.4 98.0 CH4 Conversion (mole %) 2.2 3.2 3.8 3.4 Product Selectivity CO 46.7 48.7 40.2 49.1 C2 12.4 5.4 7.6 8.0 C2H4 6.0 10.5 19.3 22.3 C2H6 28.6 28.2 25.3 15.6 C2H2 - 4.6 3.5 1.7 C3's 2.2 1.6 3.2 2.8 C4's+ 4.2 1.0 1.0 0.4 Selectivity to C +
41.0 45.9 52.3 42.8 Yield of C
0.9 1.5 2.0 1.5 Example 36 37 38 39 40 Tube Packing 20% PbO on ~-Alumina Calsicat D Silica _ (24 m2/g) Reactor Temp. (C) 757 818803 733 830 Space Velocity87008700 87006600 6600 CH4/O2 (mole ratio) 20/1 19/1 5.1/120/1 20/1 2 Conversion (mole %) 100 100 10037.9 44.1 Product Selectivity CO - 1.2 C2 48.0 44.2 55.637.4 9.7 C2H4 17.6 26.0 21.82.0 20.5 C2H6 32.8 26.2 20.860.4 68.0 2 2 ~ ~ - -C3's 1.5 2.~ 1.80.2 1.8 C4 s - - _ _ _ Selectivitv to C +
q 51.9 54.6 44.462.6 90.3 TABLE 9 (Cont'd.) Example 41 42 43 44 45 46 Tube Packing 20% PbO on Calsicat D Silica (24 m /g) Reactor Temp. (C) 835 852 872 896 915 914 Space Velocity33003300 66003300 1320 1320 CH4/O2 (mole ratio) 21/1 21/1 19/120/1 10.3/15.2/1 2 Conversion (mole %) 76.888.0 65.8 32.3100 88.7 CH4 Conversion (mole %) 6.8 8.513.4 18.7 Product Selectivity CO - - - - - 6.6 C2 9.8 9.7 8.5 9.614.2 18.3 C2H4 31.4 35.8 30.8 37.443.6 30.2 C2H6 57.0 52.2 53.2 42.426.2 20.2 C2H2 ~ ~ 2.7 2.82.0 0.0 C3's 1.8 2.4 4.8 7.57.2 19.5 C4's - - - 0.46.8 5.6 Selectivity to C
90.2 90.4 91.5 90.585.8 75.5 Yield of C

TABLE 9 (Cont'd.) Example 47 48 49 Tube Packing 17% PbO on High Surface Area Silica (245 m2/g) Reactor Temp. (C)740 740 740 Space Velocity13,040 6135 1341 CH4/O2 (mole ratio) 10/1 10/1 10/1 2 Conversion (mole %)19.9 26.1 53.0 Product Selectivity CO - - 1.6 C2 48.5 41.4 39.4 C2H4 6.9 8.2 16.3 C2H6 44-3 50.2 42.0 C3's 0.3 0.2 0.6 C4 s Selectivity to C~+
51.5 58.6 58.9 _37_ Examples 39-49 (Table 9) demonstrate the surprising influence on the oxidative coupling reaction of the phys-ical properties of the support employed in the lead oxide catalyst. By contrast to the relatively high surface area supports employed in Examples 47-49, lead oxide on Calsicat D, a low surface area silica~ afforded very high conversion of oxygen in all cases, with selectivities for the formation of coupled products in excess of 90% at CH4/O2 mole ratios of at least 19/1. Furthermore, in such examples, the selectivities for the formation of coupled products were maintained at levels of greater than 75% even at the CH4/O2 ratio of 5/1. The high sur-face area silica tube packing employed in Examples 47-49 afforded selectivities for the formation of coupled prod-ucts that were comparable to those for the ~-alumina packing employed in Examples 36-38.
To establish the influence of the surface area of the support used in preparing the oxidative coupling catalyst and of the conditions under which such support is calcined prior to impregnation, several samples of a high surface area silica (Philadelphia Quartz PQ-CD107G
SiO2) with a surface area of 239 m2/gm were calcined under various conditions (indicated in Table ~0), con-verted to catalysts, each containing 20% by weight of PbO, by precipitation of a lead compound from an aqueous solution of its nitrate in the presence of the silica and further calcination in air at about 600C to form the PbO-impregnated silica, and then evaluated as catalysts in the oxidative coupling reaction in Examples 50-54. In each evaluation, the following conditions were employed:
a reaction temperature of 750-850C, a space velocity of 6600 cc/hr/cc, and a CH4/O2 mole ratio of 20. The exper-imental parameters and results presented in Table 10 for Examples 50-54 illustrate that, as the surface area of the silica is decreased, until the surface area fell to about 21 m2/gm, there was a progressive increase in the selectivity for the production of coupled products.

Conditions of Cal- Surface cination Before Area Selectivity 5Exam~leImpreynation (m /gm) to C +

502 hrs. at 650C 239 45 518 hrs. at 830C 179 66 528 hrs. at 920C 116 85 10 538 hrs. at 970 C 21 Low Activity 544 hrs. at 1000C < 2 Inactive The catalyst prepared in Example 52 was evaluated in Examples 55-59 as a catalyst for the oxidative coupling reaction under varying conditions of reaction ternperature and space velocity. As indicated by the experimental parameters and results presented for Examples 55-59 in Table 11, the degree of oxygen conversion increased as the reaction temperature was increased at a constant space velocity and as the space velocity was decreased.
To establish the influence of the presence in the catalyst of agents, such as alkali metal components which modify the characteristics of the catalyst, such as the acidity of the support, several samples of a low surface area silica (Type 16753 manufactured by Norton Company) having a surface area of 29 m2/gm were calcined at 550-600C. with air for 2-3 hours, converted to cata-lysts, each containing 20~ PbO by weight and either no or various amounts of a sodium or magnesium component incor-porated thereinto by precipitation of a lead compound and either a sodium or magnesium compound from a solution of their nitrates in an aqueous slurry of the silica and calcination in air to form the PbO- and either Na2O- or MgO-impregnated silica. These metal-impregnated silicas were then evaluated as catalysts in the oxidative cou-pling reaction in Examples 60-118. The experimental par-ameters and results obtained are presented in Tables12-15.
The results of Examples 60-118 illustrate that a catalyst can be improved to afford a substantially higher selectivity by incorporation thereinto of a relatively small amount of a sodium component. This effect is most apparent after the catalyst has been heat treated. The incorporation of relatively higher amounts of the sodium component into the catalyst afford relatively less improvement of the selectivity of the catalyst and may promote instability of the catalyst.

s~

Example 55 56 57 58 59 Tube Packing 20% PbO on 116 m /gm Silica Reaction Temp. (C) 748 79S 849 839 856 Space Velocity 6600 6600 6600 3300 1320 CH4/O2 (mole ratio) 20.1/l 20.1/1 20.1/1 21.5/1 24.1/1 2 Conversion (mole %) 6.1 26O0 41.7 73.9 99.9 Product Selectivity CO - - - - 10.7 C2 16.0 13.7 13.1 14.4 20.1 15 C2H4 8.8 8~8 18.2 28.8 33.4 C2H6 51.8 60.0 56.8 47.9 34.4 C3's 5.1 5.1 4.8 4.2 1.5 C4's 1~.4 12.4 7.2 4.8 SelectivitY to C~+
--~.
84.1 86.3 87.0 85.7 69.3 ; 35 Example 60 61 62 63 Tube Packing20% PbO-Norton SiO2 Containing 0% Na~O
Reaction Temp. (C) 622 730 799 850 Space Velocity 1700 1700 1700 1700 (mole ratio) 24.0 24.0 24.0 24.0 2 conversion (mole %) 42.7 99.2 99.2 99.2 CH4 conversion (mole %) (1) 3.2 3.8 5O0 Product Selectivity 15 H2 (1) _ _ _ CO (1) 21.8 26.9 22~9 C2 (1) 50.7 38.5 25.1 C2H4 (1) 6.3 13.8 20.7 C2H6 (1) 19.8 17.4 18.7 C2H2 (1) - - 0.5 C3H8 (1) 1.3 0.6 1.0 C3H6 (1) 1.3 0.6 1.0 i--C (1) n-C (1) 1-C4= (1) _ _ 2.5 Unidentified C4 (1) - 2.9 8.6 Benzene (1) Selectivity to C~+
-- ~.
(1) 27.4 34.7 5~.0 Yield of C +
(1) 0.88 1.32 2.60 C~H4/C~H6 (mole ratio) 0 0.321 0.793 1.112 (1) Conversion was too low to obtain accurate selectivity measurements.

~2~

Example 64 65 66 67 68 Tube Packing 20% PbO-Norton SiO2 Containing 0.67% Na O
Reaction Temp. (C) 566 609 633 674 714 Space Velocity 16961696 1696 1696 1696 (mole ratio) 33.333.3 33.3 33.3 33.3 2 conversion (mole %) 85.198.8 99.3 98.7 99.5 CH4 conversion (mole %) 1.3 2.3 2.5 3.5 4.6 Product Selectivity CO
C2 89.560.9 53.5 42.6 47.2 C2H4 6.3 11.7 21.6 29.5 C2H6 10.529.9 32.4 27.7 18.2 C2H8 & C3H6 1.4 1.9 2.0 3.1 n-C4 - - 0.2 0.8 1.8 l C4 1.5 0.4 5.3 0.1 Unidentified C4 Benzene Selectivity to C~+
10.539.1 46.6 57.4 52.7 Yield of C ~
0.140.90 1.17 2.01 2.42 C H~/C~H6 (mole ratio) 00.2660.3600.7801.621 TABLE 13 (Cont'd.) Example 69 70 71 72 73 Tube Packing 20% PbO-Norton SiO2 Containing 0.67% Na~O
Reaction Temp. (C) 770 784 816840 853 Space Yelocity 1696 16961696 16961696 ~mole ratio) 33.3 30.630.6 30.630.6 2 conversion (mole %) 99-3 99-599 3 99 5 CH4 conversion (mole %) 4-5 5.0 6.1 6.06.3 Product Selectivity H2 - - - _11.0 CO - 3.7 1.1 3.02.8 C2 42.6 18.813.9 9.711.7 C2H4 30 7 24.030.8 33.335.8 C2H6 10.9 49.548.1 47.142.5 C2H2 1.0 0.7 0.91.2 C2H~ & C3H6 2.1 2.1 2.7 3.23.4 i-C4 n-C4 2.8 0.4 1.5 1.31.3 l-C4= 0.1 0.4 1.1 1.61.3 25 Unidentified C4 - - - - -Benzene 10.2 Selectivity to C~+
57.4 77.484.9 87.485.5 Yield o~ C~+
2.5~ 3.875.18 5.245.39 C H /C H (mole ratio) -~ 4 , 6 2.808 0.485 0.639 0.707 0.842 -4~-TABLE 13 (Cont'd.) Example 74 75 76 77 78 Tube Packing 20% PbO-Norton SiO2 Containing 0.67% Na~O
Reaction Temp. (C) 850 847851 845 861 Space Velocity 1696 3300 339033903390 (mole ratio) 30.6 24.5 24.524.824.8 2 conversion (mole %) 99.5 99.4 99.477.4 94-7 CH4 conversion (mole %) 6.2 6.8 6.15.5 6.5 Product Selectivi~y H2 10.9 8.1 1.7 CO 3.7 5.2 3.42.5 2.5 C2 10.6 12.5 12.513.010.4 C2H4 33.8 33.7 26.825.530.5 C2H6 44.3 41.3 51.654.051.3 C2H2 1.0 0.9 0.70.8 0.3

3 8 ~ C3H6 3-4 3-3 2.73.1 3.5

4 -- -- _ n-C4 1.2 1.4 1.00.5 0.8 l-C4= 1.9 1.7 1.30.5 0.8 25 Unidentified C4 - - - - -Benzene Selectivity to C~+
85.6 82.3 84.184.487.2 Yield of C +

5.31 5.60 5.134.645.67 CqH4/C~H6 (mole ratio) 0.764 0.815 0.520 0.473 0.595 ~2~

TABLE 13 (Cont'd.) Example 79 80 81 82 83 Tube Packing 20% PbO-Norton SiO2 Containing 0.67% Na O
Reaction Temp. (C) 865 855 843869 871 Space Velocity3390 3390 3390 33903390 (mole ratio)24.8 24.8 24.8 24.824.4 1~ 2 conversion (mole %) 99.6 98.9 58.0 88.494.
CH4 conversion ~mole %) 7.4 7.8 4.3 6.76.5 Product Selectivity H2 2.0 6.7 - 0.91.0 CO 2.9 2.7 2.0 2.73.6 C2 12.1 10.6 11.8 13.49.2 C2H4 32.4 42.1 24.7 31.433.7 C2H6 45.4 38.3 56.4 44.847.4 C2H2 1.0 1.4 1.1 0.60.5 C3H8 & C3H6 3.1 3.3 3~4 3.63.4 n-C4 1.7 1.0 0.3 1.41.0 l-C4= 1.3 0.3 0.3 2.11.2 25 Unidentified C4 - 0.2 Benzene - - - - -Selectivity to C~+
84.9 86.6 ~6.2 83.987.2 Yield of C +

6.28 6.75 3.71 5.625.67 C H4/C H6 (mole ratio) 0.712 1.099 0.437 0.702 0.712 TABLE 13 (Cont'd.) Example 84 85 86 87 88 Tube Packing 20% PbO-Norton SiO2 Containing 0.67% NaqO
Reaction Temp. (C) 876 886 874873 871 Space ~elocity3390 3390 3390 33903390 (mole ratio)24.4 24.4 24.4 24.424.4 ] 2 conversion (mole %) 94.7 99.5 86.7 85.282.5 CH4 conversion (mole %) 7.2 7.1 6.4 6.26.1 Product Selectivity H2 3.8 1.2 1.21.3 CO 3.4 3.8 3.3 3.13.2 C2 11.6 8.7 10.5 9.08.7 C2H4 35-3 36.9 32.2 33.031.6 C H 43.5 41.4 46.8 48.248.0 2 6 1.0 1.1 0.6 0.90.6 C3H8 & C3 6 2.9 3.8 3.3 3.43.2 i-C4 1.8 0.8 - 1.9 n-C4 1.3 1.5 1.4 1.31.3 l-C4= 1.1 1.0 1.1 1.21.4 25 Unidentified C4 - - - - -Benzene Selectivity to Cq+
85.1 87.5 86.2 88.088.0 Yield of C~+
6.13 6.21 5.52 5.465.37 C~H~/C~H6 (mole ratio) 0.806 0.893 0.688 0.684 0.660 TABLE 13 (Cont'd.) Example 89 90 91 92 Tube Packing 20% PbO-Norton SiO2 Containing 0.67~ Na2O
Reaction Temp. (C) 870 869 866 864 Space Velocity3390 3390 3390 3390 (mole ratio~24.4 24.4 24.5 24.5 O2 conversion (mole ~) 72.9 70.5 72.3 63.1 CH4 conversion (mole %) 5.8 5.9 4.7 4.5 Product Selectivity H2 1.1 0.9 CO 3.2 2.8 3.5 2.6 C2 10.3 9.9 9.1 9.1 C2H4 28.0 31.3 28.3 28.1 C2H6 46.5 45.8 53.0 53.9 C2H2 0 7 0.8 0.7 0.9 C3H8 & C3H6 26.99 2 7 3.4 3 3 l-C4 n-C4 0.8 0.5 2.1 0.5 1 C4 0.6 0.7 Unidentified C4 Benzene - - - -Selectivity to C +
86.5 87.4 87.5 88.3 Yield of C~+
5.02 5.17 4.11 3.97 C H4/C~H6 (mole ratio) 0.602 0.683 0.533 0.520 ~-48~

TABLE 13 (Cont'd.) Example 93 94 Tube Packing 20% PbO-Norton SiO2 _ Containing 0~67% Na~O
Reaction Temp. (C) 872 854 : Space Velocity3390 3390 (mole ratio~24.5 24.5 2 conversion (mole %) 70.9 57.6 CH4 conversion (mole %) 5.6 4.5 Product Selectivity H2 1.2 CO 3.0 2.4 C2 8.1 8.7 C2H4 28.2 27.3 2H6 47.3 53.2 C2H2 0.9 0.2 C3H8 & C3H6 3.2 3.5 C4 7.4 3.7 n-c4 1.2 0.5 l-C4= 0.6 0.5 Unidentified C4 Benzene Selectivity to C~
88.8 88.9 Yield of C~+
4.97 4.00 C~H~/C H6 (mole ratio) 0.596 0.513 Example 95 96 97 98 Tube Packing 20% PbO-Norton SiO2 Containin~ 1.35% NaqO
Reaction Temp. (C) 570 642 695 694 Space Velocity1696 1696 1696 1696 (mole ratio) 30.030.0 30.0 30.0 2 conversion (mole %) 3.058.9 92.8 87.8 CH4 conversion (mole %) .041.5 4.0 3.9 Product Selectivity CO
C2 10059.324.8 22.0 C2H4 (1)7.525.024.6 C2H6 (1)32.946.8 46.5 C2H2(1) C3H8 ~ C3H6(1)0.3 1.8 2.2 i-C4 (1) ~0.61.3 n-c4 (1) -1.02.5 l-C4= (1) - -0.9 25 Unidentified C4 (1) Unidentified C6(1) Selectivity to C,~
(1) 40.7 75.2 78.0 Yield of C~+
(1) 0.61 3.01 3.04 _ H ~C~H6 (mole ratio) (1) 0.229 0.534 0.530 (1) Conversion was too low for accurate measurements.

TABLE 14 (Cont'd.) Example 99 100 101 102 Tube Packing 20% PbO-Norton SiO2 Containing 1.35% Na~O
Reaction Temp. (C) 690 684682 723 Space Velocity 1696 1696 16361696 (mole ratio) 30.0 30.0 30.0 30.0 2 conversion (mole %) 82.5 75.8 70.6 99.5 CH4 conversion (mole %) 3.7 3.2 2.9 5.3 Product Selectivity CO _ _ _ _ C2 21.823.423.9 17.7 C2H4 25.023.322.3 35.9 C2H6 47.250.451.1 40.9 C3H~ ~ C3H6 1.9 1.8 1.6 2.6 i-C4 2.6 n-C4 1.2 0.8 0.7 2.6 1-C4= 0.4 0.3 0.3 0.3 Unidentified C4 Unidentified C6 Selectivity to C~+

7~.3 76.6 76.0 82.3 Yield of C~+
2.90 2.45 2.20 4.36 C H4/C H6 (mole ratio) 0.5300.462 0.437 0.879 ~25~

TABLE 14 (Cont'd.) Example 103 104 105 106 107 Tube Packing 20% PbO-Norton SiO2 Containing 1.35% Na O
Reaction Temp. (C) 624 673 715 733 789 Space Velocity 1696 1696 1696 1696 1696 (mole ratio) 29.9 29.9 29.9 29.9 29.9 2 conversion (mole %) 8.6 99.1 99.1 98~8 99.4 CH4 conversion (mole %) 0.2 3.7 4.6 4.7 9.5 Product Selectivity 15 H2 ~ - - - _ CO - Present - - -C2 56.4 26.3 29.9 23.5 32.5 C2H4 7.2 28.4 36.4 34.6 27.3 C2H6 36.4 38.8 27.3 23.8 8.4 C2H~ - 1.2 C3H8 & C3H6 2.9 2.8 2.7 2.3 4 ~ ~ - 0.2 n C4 4 0.2 0.3 0.3 Unidentified C4 - - 3.3 3.3 2.6 Unidentified C6 - - - 11.9(2) 26.7(3) Selectivity to C~+
43.6 73.6 70.1 76.6 67.5 Yield of C +
0.09 2.72 3.22 3.60 6.41 C H~/C H6 (mole ratio) 0.200 0.731 1.332 1.453 3.288 (2) Benzene and Toluene (3) Approximately 65% benzene Example 108 109 110 111 Tube Packing 20% PbO-Norton SiO2 Containing 1.66% MgO
Reaction Temp. (C)658706 757 807 Space Velocity1696169616961696 (mole ratio)31.331.331.331.3 2 conversion (mole %) 48.9 77.399.5 99.5 CH4 conversion (mole %) 0.8 1.8 2.2 2.6 Product Selectivity H2 26.2 3.2 3.0 13.9 CO - 21.838.6 34.5 C2 80.0 54.940.5 34.3 C H 4.4 8.4 6.0 11.9 c2H4 15.6 14.912.7 16.2 C3H8 & C3H6 - - 1.1 1.2 n C4 - 0.2 Selectivity to C~+
20.0 23.321.0 31.2 Yield of C~+
0.32 0.420.46 0.81 C~H4/C HG (mole ratio) 0.283 0.565 0.471 0.734 -~53-TABLE 15 (Cont'd.) Example 112 113 114 115 Tube Packing 20~ PbO-Norton SiO2 Containing 1O66~ MgO
Reaction Temp. (C) 853 876 876 785 Space Velocity1696 1696 16963390 (mole ratio)31.3 31.3 31.324.2 2 conversion (mole %) 99.5 99.5 99.599.5 CH4 conversion (mole ~) 3.0 3.0 3.3 3.2 Product Selectivity H2 47.2 70.8 63.4 4.2 CO 35.4 38.2 37.731.7 C2 25.3 20.0 22.749.0 C2~4 16.7 20.1 21.2 5.2 C2H6 16.3 17.2 14.211.4 C3H8 & C3H6 1.6 2 2 10 74lo 2 n-C4 2.9 0.2 - 0.2 l-C4= 0.2 0.3 Selectivity to C~
39.3 41.8 39.819.3 Yield of C~+
1.1~3 1.25 1.310.62 C~H~/C H~ (mole ratio) 1.028 1.319 1.495 0.465 TABLE 15 (Cont'd.) Example 116 117 118 Tube Packing 20~ PbO-Norton SiO2 Containing 1.66~ MgO
Reaction Temp. (C) 691 810 863 Space Velocity3390 3390 3390 (mole ratio)24.2 24.2 24.2 2 conversion (mole ~) 33.2 99.6 99.5 CH4 conversion (mole ~) 1.0 3.4 3.6 Product Selectivity H2 15.0 2.1 12.9 CO 8.6 32.6 42.9 C2 59.0 36.6 21.4 C2H4 7.2 10.4 10.6 C2H6 15.7 17.3 19.1 C3H8 & C3H6 5.0 1.1 0.6 i-C4 n-C4 ~ 0.1 1 C4 5.1 Selectivity to C +
32.3 30.7 35.7 Yield of C~+
0.32 1.04 1.28 C H4/C H6 (mole ratio) 0.467 0.601 0.555 Additional experiments have shown that the incorpo-ration of lithium, potassium or cesium components also affords improved selectivities of the catalysts in the oxidative coupling reaction. By contrast, incorporation of an alkaline earth metal component into the catalyst was not beneicial. Higher C2H4:C2H6 mole ratios are desirable in order to increase the yield of aromatics formed by the oligomerization of ethylene in a subsequent step, as described hereinbelow in connection with Exam~
ples 169-187.
The level of metal component on the support was found to be important within broad ranges. As can be seen from Examples 119-127, all levels of lead oxide on Calsicat D silica were effective when compared with Cal-sicat D silica without lead oxide (Examples 5-10). How-ever, the low levels of lead oxide, particularly 5.9%, tend to form some carbon monoxide at 800C as did the base silica itself, while the higher levels of lead oxide made less or none at all.
One problem with the use of lead oxide on silica is its tendency to deactivate. As illustrated in Table 10, most preferably the support is calcined before impreg-nating with the reducible metal component to obtain a catalyst of the highest selectivity. However, it is also high desirable to calcine the catalyst containing the reducible metal component at high temperature in the presence of oxygen to maintain a highly stable catalyst.
Examples 128-136 illustrate the influence of calcination after impregnation on catalyst performance. Without air calcination (Examples 128-130), activity and selectivity were high, but prolonged use o the catalyst above 800C
caused the catalyst to deactivate. When calcined in air at 1000C for 16 hours (Examples 131-133), the catalyst showed surprisingly good activity and selectivity and could be used for prolonged periods with little loss of activity. Calcination in air at 1000C for sixty hours (Examples 134-136) likewise provided a highly selective Example 119 120 121 122 123 Tube Paclcing Lead Oxide on Calsicat D Silica PbO level (wt%) 5.9% 11.1%

Reaction Temp. (C) 747 802 839 757 801 Space Velocity 1695 1695 1695 1695 1695 CH4/O2 (mole ratio) 23.5/1 23.5/1 23.5/1 23.7/1 23.7/1 2 Conversion (mole %) 72.2 99.1 99.3 60.869.0 CH4 Conversion (mole %) 3.8 7.3 8.0 2.84.4 Product Selectivity CO - 2.8 1.2 - 0.9 C2 29.1 13.4 10.6 38.421.9 C2H4 14.9 29.9 38.6 7.716.6 C2H6 54.2 50.4 44.4 50.958.8 C2H2 1.4 - 0.1 C3's 1.8 2.6 3.4 3.0 1.7 C4's and higher 0.1 0.3 Selectivity to C~
70.9 83.9 88.1 61.677.2 Yield of C
2.7 6.1 7~0 1.7 3.4 _57_ TABLE 16 (Cont'd.) Example 124 125 126 127 Tube Packing Lead Oxide on Calsicat D Silica PbO level (wt%) 11.1% 33.3%

Reaction Temp. (C) 837 757 801 837 Space Velocity 1695 1695 1695 1695 CH4/O2 (mole ratio) 23.7/] 24.0/1 24.0/1 24.0/1 2 Conversion (mole %) 99.1 47.767.399.0 CH4 Conversion (mole %) 7.6 3.75.4 7.2 Product Selectivity CO 1.7 - - -C2 12.6 13.610.2 10.1 C2H4 31.1 18.529.2 37.1 C2H6 51.1 65.757.1 46.9 C2H2 0 9 0.20.4 0.7 C3's 2.6 2.12.9 3.6 C4's and hlgher - - 0.2 Selectivity to C
85.7 86.589.8 88.3 Y ld of C
6.5 3.24.8 6.4 Example 128 129130 131 132 Calcination Temp.
(C) 600 600600 10001000 Calcination Time (hr) 16 16 16 16 16 Air no no no yes yes Reaction Temp. ( C) 721 807 822745 831 10Space Velocity1700 17001700 17001700 CH4/O2 (mole (rate) 18.5/1 18.5/1 18.5/1 23.4/1 23.4/1 2 Conversion (mole %) 71.1 95.295.0 68.799.5 CH4 Conversion (mole %) 4.5g.o Product Selectivity CO - - 1.8 - 1.5 C2 21.1 14.012.7 20.9 9.7 20C2H4 14.8 36.342.2 17.834.1 C2H6 39.4 44.730.9 59.641.7 2 2 ~ ~ 0 7 ~ 0 4 C3's 4.1 3.24.7 1.6 2.9 C4's and higher20.7 1.77.1 - 11.4 Selectivity to C~
79.0 85.985.6 79.090.5 Yield of C~
3.6 8.1 ~2~

TABLE 17 (Cont'd.) Example 133 134 135 136 Calcination Temp.
(C) 1000 1000 1000 1000 Calcination Time (hr) 16 60 60 60 Air yes yes yes yes Reaction Temp.
(C) 856 723 825 863 Space Velocity170017001700 1700 CH4/2 (mole ratio) 23.4/1 24.2/1 24.2/1 24.3/1 2 Conversion (mole %~ 99.5 9.7 68.5 99.1 CH4 Conversion (mole %) 8.2 0.7 5.5 7.4 Product Selectivity CO - - 2.5 3.8 CO2 10.2 15.2 9.5 8.5 C2H4 43.2 5.4 31.8 42.1 C2H6 39.9 72.0 52.0 39.9 C2H2 - ~ 1.3 1.7 C3's 3.8 7.5 2.9 3.7 C4's and higher 1.0 - - 0.4 SelectivitY to C~~~
-- c.
87.984.9 88.0 87.8 Yield of C +
7.2 5.9 4.8 6.5 ~s~

and stable catalyst, although some of its original activity was lost, particularly at low coupling tempera-tures. It is believed that lead oxide in calcination reacts with the silica base to form some form of lead silicate. In the presence of air this compound presum-ably is maintained in its highest valence state.
The conditions employed to calcine the oxidative coupling catalysts employed in Examples 5-27 and 32-187 are summarized in Table 18.
Other lead compounds have been shown to give good selectivities for the formation of coupled products, depending on the nature of the anion. Lead sulfate (Examples 137-141) was relatively unattractive until it was exposed to prolonged reaction conditions. During this period, SO2 was evolved making a new and more selec-tive species. Lead sulfide (Examples 142-144) was active from the beginning and afforded high selectivity for the formation of coupled products but tended to deactivate with time. Lead tungstate (Examples 145-147) was moder-ately selective at low temperatures. Lead molybdate(Examples 148-149) was much less selective even at low temperatures. In each of Examples 137-149, the lead com-pound was supported on a Calsicat D support. Preferred anions are those that can decompose to form a lead oxide type of compound.
Catalysts containing compounds of reducible metals other than lead are less selective when tested in the oxidative coupling reaction under similar conditions.
For example, vanadia on Calsicat D silica afforded only a 22% selectivity for the formation of coupled products.
Manganese oxide on Calsicat D silica afforded 50-64%
selectivity for the formation of coupled products.
Indium oxide on Calsicat D silica afforded a 31-45%
selectivity for the formation of coupled products.

All of the examples of the oxidative coupling reac-tion presented in Examples 1-149 were performed using a 5~i~8 Conditions of Surface Area Conditions of Calcination (m2/gm) Calcination Before Before After ExampleImpregnationImpregnationImpregnation 5_1018 hrs at 1000C 24 11-131 Used as received <5 14-17 Used as received 24 1018-211 2 hrs at 600C <5 22-251 2 hrs at 600C 44 261 2 hrs at 600C
271 2 hrs at 600C
32_351 2 hrs at 743C
1536-38 -- 4 2 hrs at 600C
39-46 Used as received 24 2 hrs at 600C
47-49 Used as recelved 245 2 hrs at 600C
2 hrs at 650C239 2 hrs at 600C
51 8 hrs at 830C179 2 hrs at 600C
20 52 8 hrs at 920C116 2 hrs at 600C
53 8 hrs at 970C 21 2 hrs at 600C
54 4 hrs at 1000C<2 2 hrs at 600C
55-59 8 hrs at 920C116 2 hrs at 600C
60-118 2-3 hrs at 550-660C - 2 hrs at 600C
25119-127 Used as received 24 2 hrs at 600C
128-130 Used as received 24 16 hrs at 600C
131-133 Used as received 52 16 hrs at 1000C
134-136 Used as received 4Z 60 hrs at 1000C
137-168 Used as received 24 2 hrs at 600C
30181-188 Used as received 24 2 hrs at 600C

1 Not impregnated 2 Surface area after impregnation 5~

Example 137 138139 140 141 Tube Packin~ 20% PbSO4 Reaction Temp. (C) 715 756 803 842 830 Space Velocity1695 1695 1695 1695 3390 CH4/O2 (mole ratio)22.7/1 22.7/1 22.7/1 22.8/1 22.1/1 2 Conversion (mole %) 99.4 99.399.4 99.2 99.4 CH4 Conversion (mole %) 8.5 7.36.9 7.3 8.3 Product Selectivity CO - - 0.3 1.7 3.4 C2 58.5 31.919.9 17.0 12.2 C2H4 7-3 16.730.5 42.7 32.9 C2H6 28.6 36.745.5 32.8 47.6 H - - 0.6 0.5 0.7 ~2 2 C3's 1.0 2.42.3 4.0 2.9 C4's+ 4.6 12.30.9 1.3 0.2 Selectivity to C~+
41.5 6B.179.8 81.3 84.3 Yield of C
3.5 5.05.0 5.9 7.0 ~s~

TABLE 19 (Cont'd.) Example 142 143 144 Lead Compound20% PbS

Reaction Temp. (C) 757 805 858 Space Velocity 1690 1690 1690 CH4/O2 (mole ratio) 23.0/1 23.1/1 23.1/1 2 Conversion (mole %)82.7 99.099.4 CH4 Conversion (mole %)6.4 7.38.7 Product Selectivity C2 20.5 13.110.3 C2H4 19.4 32.642.2 C2H6 55.6 51.234.6 C2H2 0.1 0.42.3 C3's 1.8 2.84.3 C4's+ 1.2 - 6.4 SelectivitY to C
78.1 87.089.8 Yield of C~+
5~0 6.47.8 TABLE 19 (Cont'd.) Example 145 146 147 148 149 Tube Packing 20% PbWO~ 20~o PbMoO~

Reaction Temp. (C) 742 807 879 763 863 Space Velocity 3390 3390 3390 1695 1695 CH4/2 (mole ratio) 22.3/1 22~3/1 22~3/1 23.8/1 23~8/1 10 2 Conversion (mole %) 62.4 99.399~1 99.4 99.0 CH4 Conversion (mole %) 3.2 5~47.3 3.6 4.7 Product Selectivity CO ~ 7.444~5 6.7 43.9 C2 36.5 36.126 ~ 765.5 40.3 C2H4 8~1 12~35~4 2.6 2.7 C2H6 51.1 42~421~4 24.6 10.8 C2H2 1.5 ~0 ~ 9 ~ 1.6 C3's 2.2 1.81.0 0.6 0.7 4 s 0.7 Selectivity to C
63.6 56~528.7 27~8 15.8 Yield of C
..
1.9 3.12.1 1.0 0.7 once-through operational mode, with no attempt being made to recover and recycle the unreacted feedstock alkane.
In order to increase the conversion of the feedstock alkane and the yield of desired products therefrom, it is desirable to recycle unused feedstock alkane. However, the use of simple recycle of the entire product mixture formed in the oxidative coupling reaction is not particu-larly advantageous as shown in Examples 150-155. Exam-ples 150-155 were performed using the same general procedure as used in Examples 39-46, except that in Exam-ples 154-155 the product was recycled. The catalyst employed in Examples 150-155 was a Calsicat D silica sup-port (that had not been calcined prior to impregnation) containing 20% by weight of PbO that was calcined for 2 hours at 600C after impregnation.
Examples 150-153 show the performance of a lead oxide catalyst on Calsicat D silica in a once-through mode. As is seen, even at the lowest CH4/O2 mole ratio of 5.2/1 (Example 153), the selectivity for the formation of coupled products was respectable, but the conversion of methane and yield of coupled products were at best only about 19% and 14%, respectively.
Surprisingly, however, when the entire gaseous product mixture from the oxidative coupling reaction was recycled to the oxidative coupling step (Examples 154-155), selectivity for the formation of coupled prod-ucts dropped drastically into the range of 42-61%, even with high mole ratios of CH4/O2 in the total incoming gas, and the yield of coupled products ~obtained as the product of the CH4 conversion multiplied by the selec-tivity for the formation of coupled products, divided by 100) was no better than with once-through operations.

Examples 156-168 involve a systematic study to find the components in recycle gas that are responsible for this undesirable effect illustrated in Examples 154-155.
Examples 156-168 were performed using the same general Example 150151 152 153 154 155 Reaction Temp. (C) 829 896 915 914836 836 Space Velocity6600 3300 13201320 1690 1690 Recycle No Yes CHa/O2 (mole 18.7/1 19.9/1 10.3/1 5.2/1 8.4/1 8.4/1 ratio) in makeup feed CH4/O2 (mole 18O7/1 19.9/1 10.3/1 5.2/1 33.2/1 24.5/1 ratio) in total feed 2 Conversion (mole ~) 33.7 92.3100.0 88.7 96.4 94.9 CH4 Conversion (mole ~) 3.4 8.513.4 18.7 9.5 22.0 Product Selectivity CO 0.0 0.0 0.0 6.6 6.5 6.7 C2 8.3 9.614.2 18.3 32.9 51.1 C2H4 19.7 37.443.6 30.2 32.7 25.3 C2H6 70 4 42.426.2 20.2 14.0 9.8 C2 2 2.8 2.0 0.0 0.7 0.6 C3's 1.7 7.5 7.2 19.5 4.7 3.2 C4's 0.0 0.4 6.8 5.6 8.0 2.7 Selectivity to Cq 91.8 90.585.8 75.5 60.1 41.6 Yield of Cq 3.1 7.711.5 14~1 5.7 9.2 procedure as used in Examples 39-46, except as indicated herein. The catalyst employed in Examples 156-168 was a Calsicat D silica support (that had not been calcined prior to impregnation) containing 20% by weight of PbO
that was calcined for 2 hours at 600C after impregna-tion. By spiking methane feed to the oxidative coupling reaction with nitrogen, carbon monoxide, carbon dioxide and water, it was observed that none of these materials had a deleterious eEfect. Residual olefins and acetylene in the recycle gas, however, did have an undesirable effect in the oxidative coupling reaction. Ethane itself did not. The effect of ethane in the oxidative coupling reaction is shown in Examples 156-161. The use of blend of 10% ethane and 90% methane as feedstock afforded a surprising increase of both selectivity and yield for ethylene and higher products. Even a 100% ethane feed-stock was converted to unsaturates in high selectivity and yield. ~ccountability of carbons across the system was essentially 100%, indicating little tendency to form coke. On the other hand, the presence of ethylene in the feedstock to the oxidative couling reactor had a deleter-ious effect, even at levels of 1% in methane, as shown in Examples 162-168. Of particular concern was the observa-tion that accountability of carbons across the system was poor, as a result of coke formation. Thus, in order to increase the degree of conversion of the feedstock alkane and the yield of the desired products therefrom, the recycle gas must be substantially free of ethylene and other higher unsaturates to preserve the high selectivity of an oxidative coupling catalyst for methane coupling, but it is advantageous that ethane is present in the feed or recycle.

It was surprisingly observed that certain acid cata-lysts were able to remove ethylene and higher unsaturates from very dilute methane streams even at atmospheric pressure and that this reaction gave rise to high yields ~z~

Examples 156 157 158 159 160 161 Feed 10% C,HG in CH4 100% C HG
Reaction Temp. (C) 783 838 847739787 823 Space Velocity 6600 6600 33006600 6600 6600 C~14/216.8/1 16.8/1 17.6/1 (mole ratio) C2H6/2 1.76/1 1.76/1 1.89/1 11.5 11.5 5.4 (mole ratio) 2 Conversion 30.085.3 10059.2100 100 (mole %) C2H6 19.2 44.266.5 9.727.362.5 Conversion (mole %) Product Selectivity CO - - - 0.152.1 3.9 C2 6.9 5.4 3.3 1.30.6 0.8 CH4 2.42.9 5.2 20 C~H4 89.6 89.286.2 92.088.284.0 C2H - - _ _ _ _ C H - 0 8 2.3 - 2.5 3.0 C3's 3.5 4.7 6.3 4.11.8 2.2 C4's 2.0 - 2.0 0.8 Selectivity to Cq 93.1 94.796.8 96.194.590.0 Yleld of C
17.9 41.964.3 9.325.856.3 Example 162 163 164 165 Feed, % 2 4 4 0.8 1.4 10 Temp. (C) 815 814 811 746 Space Velocity 6600 66006600 6600 CH4/2 24.1/1 25.9/1 27.3/1 18.0/1 (mole ratio) C2H4/2 ~ 2.3/1 (mole ratio) 2 Conversion 52.664.4 67.385.0 (mole %) C2H4 Conv. (mole ~) - ~ ~ 14.7 Product Selectivity 15 CO - - - 1.4 CO 8.515.6 18.125.1 C2H4 28.0 15.12.4 C2H6 47.8 47.961.1 26.0 2 2 ~ ~ 4-3 4-7 C3's 15.8 17.38.9 9.9 C4's+ - - 5.2 32.9 Selectivity to C
, 91.6 80.381.9 73.5 ~25~

TABLE 22 (Cont'd.) Example 166 167 168 Feed, % C2H4 in CH4 lO100 lO0 Temp. (C) 795 733 836 Space Velocity 6600 6600 3300 CH4/2 18.0/1 - -(mole ratio) C2H4/2 2.3/1 16.8/l 2.3/1 (mole ratio) O~ Conversion99.771.8 100 (mole %) C2H4 Conv. (mole %)20.6 4.2 62.6 Product Selectivity CO 0.144.1 29.0 C2 21.9 ? 16.1 CH4 ~ 9.0 16.1 C2H6 27.8 7.9 4.8 C2H2 6.2 5.9 1.9 C3's 13.826.1 5.6 C4's+ 30.3 7.0 20.9 Selectivity to C
78.146.9 33.2 of recoverable aromatic hydrocarbons. While it had been known that metal-exchanged zeolites do oligomerize eth-ylene to form higher molecular weight olefins under pres-sure, we found that such catalysts are ineffective under conditions of low pressure and low concentration. Simi-larly, an alumina catalyst containing vanadium oxide and palladium and reported by A.B. Evin, et al, J. of Cata-lysis, 30, 109-117 (1973) for the oxidative conversion of ethylene to acetaldehyde, was employed in the oligomeri-zation reaction with a synthetic mixture containingnitrogen, oxygen, methane, acetylene, ethylene, ethane and traces of C3 and C4 paraffins and olefins, but was found to convert only 14-56% of the ethylene at very low space velocities. ~hen used with the same mixture in the oligomerization reaction, concentrated sulfuric acid was effective only for the conversion of higher olefins.
Only zeolitic materials in the acid-exchanged form showed appreciable activity in the oligomerization reac-tion. A number of the most effective materials are shown in Examples 169-180. Examples 169-176 involve a catalyst which is a composite of 35 weight percent of alumina and 65 weight percent of one of two acidic borosilicate molecular sieves made in accordance with preparations disclosed in Haddid, European Patent Application No.
82303246.1. A borosilicate sieve of relatively low acidity was employed in Examples 169-172. It gave good conversion of ethylene at low space velocities, complete acetylene conversion at all space velocities tested and complete or nearly complete conversion of propylene under most conditions. Although products above C5 were not measured in these studies, the buildup of higher hydro-carbons was observed. A borosilicate of stronger acidity was employed in Examples 172-176 and was more effective than the less acidic borosilicate, giving 80-90% conver-sion of ethylene over a wide temperature range at ahigher space velocity. ZSM-5, the strongest acidic zeol-itic material tested, was employed in Examples 177-180 T~BLE 23 Examples 169 170 171 172 Temp. (C) 396 353 337 321 Space Velocity 191 96 49 44 Feed Component Percent Percent Removed in Product N2 48.8 0 0 0 0 CH4 47.00.4 0 0.9 1.6 C2 0-490 7 ~0-9 0.2 -7.2 2 0 990 3 -0.8 -O.S -1.1 C2H4 1.0134.657.7 78.5 91.8 C2H6 1.0~1.7 0.4 0.2 -11.4 C2H6 0.13100 81.7 100 100 C3H8 0.10 -103 C3H6 0.1116.784.4 100 100 I-C4 0.11-72.7-47.8 -83.7 -222 N-C4 0.06-116 -59.7 -43.5 -0.3 C4+ 0.27-19.1 -1.6 6.4 -135 1 A negative value indicates an increase in that component.

~L2~r,~

TABLE 23 (Cont'd.) Examples173 174 1752 1762 Temp. (C) 296 317 310 365 Space Velocity 360 360 360 360 : Feed ; Component Percent Percent Removed in_Product N2 4~ 9 CH4 47.0-0.8 -0.9 0.4 -0.3 C2 0 505.6 6.8 -20.5 -14.0 2 1.00-1.0 -1.0 -0.8 -0.6 C2H4 1.0079.989.9 88.5 87.3 C2H6 1.00-1.8 -2.8 -2.3 -3.3 C2H6 0.01100 100 100 100 C3H8 0.10-97.1 -lS0 -74.8 -150 C3H6 0.10100 93.5 100 100 I-C4 0.10-79.6-94.7-124.1 -94.5 N-C4 0.1024.522.0 18.9 19.7 C4~ 0.10-9.6 -14.5 -29.9 31.4 1 A negative value indicates an increase in that component.
2 Water was added with the feed at about 10 moles per mole of ethylene.

~2~

TAsLE 23 (Cont'd.) Examples 177 178 1792 18o2 Temp. (C) 296 301 309 292 Space Velocity 360 1440 720 1440 Eeed Component Percent Percent Removed in Product N2 48.9 0 0 0 0 CH4 47.0-0.8 -0.3 0.5 0.2 C2 0-5023.7 11.7 2.3 0.7 2 1.00-0.4 -0O3 1.6 -1.4 C2H4 1.00100 95.0 99.0 96.1 C2H6 1.00-1.3 -0.7 -2.4 -1.7 C2H6 0.01100 100 100 100 C3H8 0.10-142 -183 -150 -138 C3H6 0.10100 100 100 100 I-C4 o.10-172 -152 -179 -161 N-C4 0.1030.517.6 30 30.2 C4+ 0.10-14.5-30.3 -37.8 -2.3 1 A negative value indicates an increase in that component.
2 Water was added with the feed at about 10 moles per mole of ethylene.

~z~
-75~

and was especially effective, giving 95-100% conversion of ethylene at space velocities in the range of 269-1440.
Water was found not to be detrimental to the olefin con-version, as indicated by Examples 175-176 and 179-180.
To show the effect of the oligomerization of unsatu-rates on the effectiveness of recycle to the oxidative coupling reaction, a packed column of H-ZSM-5 was employed in Examples 181-189 at the outlet of the oxida-tive coupling reactor to oligomerize the unsaturates in the product stream, higher products were largely removed with a dry-ice acetone trap, and the remaining gases were recycled back to the oxidative coupling reactor. The oxidative coupling catalyst employed was a Calsicat D
silica support (which had not been calcined prior to being impregnated) containing 20 percent by weight of lead oxide and which had been calcined in air at about 600C for 2 hours after impregnation.
By comparison to the results of Example 155 where olefins in the feed to the oxidative coupling reactor were not oligomerized, in Examples 181-188, there was a noticeable improvement in methane conversion, selectivity for the production of coupled products and yield of cou-pled products in the oxidative coupling reaction. Fur-thermore, liquids in large quantities were condensed out of the system.
To demonstrate that small amounts of oligomerization products and higher molecular weight coupled products remaining in the recycle after oligomerization and after the dry ice-acetone trap were detrimental to the oxida-tive coupling reaction, the recycle stream was passedthrough a bed of granular coconut charcoal after passing through the dry-ice trap and before being returned to the oxidative coupling reactor. The effect of this is seen in Examples 185-188. By the simple addition of a char-coal bed, methane conversions, selectivities for the for-mation of coupled products and yields of coupled products increased to 63-82%, 78-85% and 53-67%, respectively.

Example 155 181 182 183 184 Special Conditions Without Charcoal Oxid. Coup.
Temp. (C) 836 806 824 810 853 Oxid. Coup.
Space Velocity 1690 1690 1690 2618 1960 Recycle yes yes yes yes yes 10 Oligomerizationno yes yes yes yes Olig. Temp. (C) - 285 285 285 285 Olig. Space Velocity - ~1400 ~1400 ~1400~1400 CH4/O2 (mole ratio) in makeup feed 8.4/1 4.2/1 4.0/1 2.3/1 1.43/1 CH4/O2 (mole ratio) in total feed 24.5/1 23.2/1 26.1/1 18.3/1 16.4/1 2 Conversion (mole %) 94.9 94.4 95.0 99.5 99.4 CH2 Conversion (mole %) 22.0 32.2 27.9 49.1 62.9 Product Selectivity CO 6.7 2.2 0.9 o.t3 1.2 C2 51.1 17.2 15.8 30.5 35.2 - 25 C2H4 25.3 0.0 0.1 0.0 0.2 C2H6 9.8 7.6 7.6 5O9 3.1 C2H2 0.6 0.0 0.0 0.0 0.0 C3's 3.7 0.9 1.8 1.1 0.7 C4's 2.7 3.8 8.8 2.8 2.1 Li~uids - 68 66 59 57 Selectivity to C
42.1 80.6 83.3 68.8 63.6 Yield of C

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TABLE 24 (Cont'd.) -Example 185 186 187 188 Special Conditions With Charcoal Oxid. Coup.
Temp. (C) 854 858 847 809 Oxid. Coup.
Space Velocity2618 2618 1960 1940 Recycle yes yes yes yes 10 Oligomerizationyes yes yes yes Olig. Temp. (C) 285 2-35 285 285 Olig. Space Velocity ~1400 ~1400 ~1400 ~1400 CH4/O2 (mole ratio) in makeup feed 1.92/1 1.92/1 1.52/1 1.47/1 CH4/O2 (mole ratio) in total feed13.6/1 13.6/1 14.3/1 7.2/1 2 Conversion (mole %) 96.8 99.1 99.4 98.6 CH4 Conversion (mole %) 63.1 64.9 72.5 81.6 Product Selectivity CO 0.6 0.8 0.7 0.0 C2 14.8 17.8 21.6 17.8 C2H4 0.2 0.2 0.1 O.o C2H6 3.3 3.3 2.6 1.7 C2H2 0.0 0.0 OoO 0~0 C3's 0.5 0.6 0.4 0.4 C4's 2.1 4.1 1.0 0.0 Liquids 79 53 56 67 Selectivity to C~
84.6 81.4 77.7 82.2 Yield of C
L.

~0 Since air is added to the system in the oxidative coupling step, a slip stream of the recycle gas is vented to prevent a buildup of nitrogen in the gas that is recy-cled to the oxidative coupling step. The slip streamwhich is vented contains about 10-20~ of the methane originally charged to the reactor. We have found that, by passing the slip stream through a bed of coconut char-coal, not only is the methane recovered, but also both nitrogen and carbon dioxide in the slip stream are vented and prevented from building up in the recycle gas. As a mixture of nitrogen, carbon dioxide, methane, and ethane was passed through a bed of coconut charcoal, a stream of nitrogen largely devoid of hydrocarbons passed out of the bed. As the adsorption was continued, the other compo-nents of the stream passed out of the bed in this order-methane, carbon dioxide, and ethane. When the bed became saturated with methane, methane began to pass out of the bed, and the charcoal bed was removed from service and replaced in service by a fresh charcoal bed. The compo-nents adsorbed on the saturated bed were desorbed with vacuum, in the order: methane, carbon dioxide, and ethane. Hence, by judicious use of vacuum, fractions rich in methane, carbon dioxide and ethane were isolated.
The desorbed methane is returned back to the system, and nitrogen and carbon dioxide rejected, thus permitting a nearly complete return of methane to the system with high ultimate conversion and a minimal buildup of nitrogen and carbon dioxide in the system. With about a 20-minute adsorption of components from the slip stream and a 10-minute desorption of the adsorbed methane, a charcoal bed was able to be placed on a fast cycle for economic separation of components.

From the above description, it is apparent that the objects of the present invention have been achieved.
While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of the present invention.
Having described the invention, what is claimed is:

~ ..

Claims (29)

CLAIMS:

1. An oxidative coupling catalyst comprising a reducible compound of lead, antimony, vanadium, germa-nium, tin, bismuth, cadmium, indium, manganese or thal-lium or a mixture thereof and a support comprising silica having a surface area less than about 175 m2/gm, wherein the reducible compound is at a level of from about 2 to about 50 weight percent, calculated as the oxide of the reducible metal and based on the weight of the catalyst.

2. The oxidative coupling catalyst of Claim 1 wherein the reducible metal compound is at a level of from about 10 to about 30 weight percent, calculated as the oxide of the reducible metal and based on the weight of the catalyst.

3. The oxidative coupling catalyst of Claim 1 wherein the reducible metal compound is an oxide, sul-fide, sulfate or carbonate.

4. The oxidative coupling catalyst of Claim 1 com-prising a reducible compound of lead.

5. The oxidative coupling catalyst of Claim 4 wherein the reducible lead compound comprises lead oxide.

6. The oxidative coupling catalyst of Claim 1 wherein the reducible compound ls lead oxide.

7. The oxidative coupling catalyst of Claim 1 wherein the support is silica.

8. The oxidative coupling catalyst of Claim 1 wherein the silica has a surface area of from about 5 to about 75 m2/gm.

9. The oxidative coupling catalyst of Claim 1 wherein the support is calcined at a temperature of from about B00°C to about 1100°C for from about 2 hrs. to about 36 hrs. before the reducible metal compound is incorporated into it.

10. The oxidative coupling catalyst of Claim 9 wherein the support is calcined at a temperature of from about 950°C to about 1050°C for from about 4 hrs. to about 16 hrs. before the reducible metal compound is incorporated into it.

11. The oxidative coupling catalyst of Claim 1 wherein the support containing the reducible metal com-pound is calcined at a temperature of from about 500°C to about 1050°C for from about 2 hrs. to about 36 hrs.

12. The oxidative coupling catalyst of Claim 11 wherein the support containing the reducible metal com-pound is calcined in air at a temperature of from about 950°C to about 1050°C for from about 4 hrs. to about 20 hrs.

13. The oxidative coupling catalyst of Claim 1 com-prising additionally an alkali metal component at a level of from about 0.1 to about 6 weight percent calculated as the alkali metal oxide and based on the weight of the catalyst.

14. The oxidative coupling catalyst of Claim 13 wherein the alkali metal component is at a level of from about 0.5 to about 3 weight percent, calculated as the alkali metal oxide and based on the weight of the cata-lyst.

15. A method for converting at least one feedstock alkane containing from 1 to 3 carbon atoms to heavier hydrocarbons, comprising: contacting the feedstock alkane with an oxygen-containing gas in a reactor in the presence of the oxidative coupling catalyst of Claim 1 at a temperature in the range of from about 600°C to about 1,000°C.

16. The method of Claim 15 wherein the feedstock alkane is contacted with the oxygen-containing gas at a temperature in the range of from about 700°C. to about 850°C.

17. The method of Claim 15 wherein the feedstock alkane is contacted with the oxygen-containing gas under a total absolute pressure in the reactor in the range of from about 1 atm. to about 10 atm.

18. The method of Claim 15 wherein the ratio of the combined feedstock alkane partial pressure-to-the oxygen partial pressure at the entrance to the reactor is in the range of from about 2:1 to about 40:1.

19. The method of Claim 15 wherein the feedstock alkane is contacted with the oxygen-containing gas at a space velocity of from about 100 to about 10,000 volumes of total feed gas per volume of catalyst per hour.

20. A method for converting at least one feedstock alkane containing from 1 to 3 carbon atoms to heavier hydrocarbons, comprising: contacting the feedstock alkane with an oxygen-containing gas in a reactor in the presence of an oxidative coupling catalyst at a temperature in the range of from about 600°C to about 1,000 C, wherein the oxidative coupling catalyst comprises a reducible compound selected from the group consisting of lead, antimony, vanadium, tin, bismuth, cadmium, manganese and thallium and a mixture thereof on an amorphous refractory inorganic oxide support comprising silica having a surface area in the range of from above about 21 m2/gm to about 175 m2/gm.

21. The method of claim 20 wherein the feedstock alkane is contacted with the oxygen-containing gas at a temperature in the range of from about 700°C to about 850°C.

22. The method of claim 20 wherein the feedstock alkane is contacted with the oxygen-containing gas under a total absolute pressure in the reactor in the range of from about 1 atm. to about 10 atm.

23. The method of claim 20 wherein the ratio of the combined feedstock alkane partial pressure to the oxygen partial pressure at the entrance to the reactor is in the range of from about 2:1 to about 40:1.

24. The method of claim 20 wherein the feedstock alkane is contacted with the oxygen-containing gas at a space velocity of from about 100 to about 10,000 volumes of total feed gas per volume of catalyst per hour.

25. A method for converting at least one feedstock alkane containing from 1 to 3 carbon atoms to heavier hydrocarbons, comprising: contacting the feedstock alkane with an oxygen-containing gas in a reactor in the presence of an oxidative coupling catalyst at a temperature in the range of from about 600°C to about 1,000°C, wherein the oxidative coupling catalyst comprises a reducible compound of lead on an amorphous refractory inorganic oxide support comprising silica having a surface area in the range of from above about 21 m2/gm to about 175 m2/gm.

26. The method of claim 25 wherein the feedstock alkane is contacted with the oxygen-containing gas at a temperature in the range of from about 700°C to about 850°C.

27. The method of claim 25 wherein the feedstock alkane is contacted with the oxygen-containing gas under a total absolute pressure in the reactor in the range of from 1 atm. to about 10 atm.

28. The method of claim 25 wherein the ratio of the combined feedstock alkane partial pressure to the oxygen partial pressure at the entrance to the reactor is in the range of from about 2:1 to about 40:1.

29. The method of claim 25 wherein the feedstock alkane is contacted with the oxygen-containing gas at a space velocity of from about 100 to about 10,000 volumes of total feed gas per volume of catalyst per hour.